Magnetic shield for watches



(No Model.)

H. P. PRATT.

MAGNETIC SHIELD EOE WATCHES. 110.403,211. Patented May 14, 1889.

N PETERS. Phowumlnpur, wnhzngian. D4 C.

UNITED STATES PATENT OEEICE.

HARRY P. PRATT, OF CHICAGO, ILLINOIS.

MAGNETIC SHIELD FOR WATCHES.

SPECIFICATION forming part of Letters Patent No. 403,211, dated May 14, 1889.

Application filed December 8, 1885. Serial No. 185,059. (No model.)

To all whom, t may concern.-

le it known that I, HARRY P. PRATT, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a cert-ain new and useful Magnetic Shield for Iatchesg and I hereby declare the following to be a full, clear, and exact description of the same.

My invention relates to a device comprising a shield, or in the nature of a shield, to form a permanent part of a watch, which shall operate, by its inherent property, to prevent the inclosed movement from being affected by any degree of adjacent magnetic or electrical inliuence, including the magnetic iniiuence of the earth. Shields for a somewhat similar purpose are not broadly new, for I am aware of the existence of one such device which is patented, and comprises, broadly, a shield formed of a material highly sensitive to magnetic influence, (but not itself a permanent magnet,) wholly or in part surroimding and inclosing the movement within the case. The effect desired from the use of such a shield is to receive the magnetic influence upon itself and thereby avoid its contact with the watchworks, which function it may perform till it shall become oversaturated with magnetisl'n, when, as experience shows, it ceases to shield.

My invention consists in a device for the purpose :formed wholly or `in part of a permanent magnet, which operates to shunt any external magnetic influence brought into contact with it, the effect of which is merely to intensify the magnet, and the movement, being surrounded by the magnet, occupies a neutral iield, and is thus outof rca-ch of the magnetic influence. I

Myinvent-ion further consists in certain details of construction and combinations of parts, all as hereinafter more fully set forth.

Referring' to the drawings, Figure l is a plan view of a continuous ring surrounding works of a watch and formed of a permanent magnet, and comprising the most simple and therefore preferred form of my device; Fig. 2, a similar view of a ring formed of al permanent magnet having its poles joined; Fig. i3, a plan view of a modification con'iprising a similar ring 'formed in sections having opposite poles 0n each section joined by brazing; and Fig.

i, a sectional view of a shield formed in any one of several ways, each of which affords a modiiication of the ring shown in Fig. l.

A is a natural or other permanent magnet in the form of a continuous ring, having its poles N S joined, preferably by bracing, and encircling watch-works B. It occupies the position of the usual dust-band and performs, incidentally, the functions of a dustband. A watch provided with such a ring or shield is unaii'ected in its movement when brought into contact with a very powerful magnet or placed directly upon the poles of a` powerful dynal11o-machine, each of which experiments has repeatedly been performed, the dynamo referred to being used. to supply six arc lamps, and in no instance was there any disturbing effect produced in the watch-works. It is also a fact that my improved device prevents inliuence upon a watch-movement provided with it of vthe ever-present earth-magnetism, as the balance-wheel works much more freely with the device than without it.

The effect of the permanent magnet forming the shield is to shunt the external magnetic iniuence whereby the magnet becomes intensified; but the watch-movement remains ui'laffected, since the neutral quality of its position between the poles is unchanged, and the same result appears when the shield comprises any other form of permanent magnet than that of a natural one or loadstone. It may be 'formed in parts more than one, as indicated in Fig. 3, with the opposite poles of each two sections adjoining each other; and the device may comprise the construction shown in Fig. e, wherein the ring A is of soft metal provided with a permanently-magnetized plate, C, or natural magnet constituting the plate, covering its upper or lower edge, when the opposite edge may be surmounted by a metal plate, C', which, with the ring A, forms the armature. The last-named device forms a shield which completely envelops the watch-movement; and this device when used may be provided with a metallic, originally non-magnetized, cap, I), to cover the permanent magnet C and serve to prevent any tendency to demagnetization.

It is impracticable and perhaps impossible to describe all of the various modifications IOO which may serve the purpose of my device by the embodiment with them of my invention, which consists, broadly, in preventing the magnetization of the Works of a Watch by shieldingl them with a permanent magnet;

but all such modifications or devices having a permanent magnet to serve the purpose are included Within my invention..

What I claim as new, and desire to secure by 1o Letters Patent, is-

1. A Watch-movement partially or Wholly surrounded by a permanently-magnetic shield whereby a'magnetio current ioWs constantly around the movement, substantially as and for the purpose Set forth.

2. A Watch-movement surrounded by a permanently-magnetic continuous ring, A, substantially as and for the purpose set forth.

HARRY P. PRATT.

In presence of- MASON BRoss, WM. SADLER. 

